Depending on the particular application, i.e. which type of vehicle, a crash or collision with another vehicle or an obstacle, the direction and magnitude of a shock, the efforts to make to sufficiently protect a passenger against injuries are different, but sensing and evaluating the crash has to be done in the range of milliseconds to have enough time to inflate or to tension the a.m. restraint system. An igniting device must be activated in order to ignite a fuel charge or propellant in the gas generator when triggered.
Because electronic sensor systems could sense and evaluate quite a lot of eventualities with respect to vehicle types and types of crash, they become more and more widespread in practice. However electronic sensor systems have the disadvantage that electromagnetic waves, high- or ultra high frequencies (HF, UHF), can influence their well-functioning. An example of such influence is when a vehicle having such an electronic sensor system built into it, moves in traffic nearby a radio station, a tv station, or similar source of electronic noise and/or disturbances.
For safety reasons such electronic sensor systems in the art use an additional mechano-electrical switch, normally open, and closed only when a substantial velocity change in the vehicles move occurred, or there has been used two independent but redundant electronic sensor circuits.